<!DOCTYPE html>
<html>
<head>
    <title></title>
    <script src="http://code.jquery.com/jquery-3.2.1.min.js"></script>
</head>
<body onload="draw()">
    <canvas id="mycanvas" width="150" height="150"></canvas>
    <script>
        // 二次曲线
        function draw() {
            // 获取canvas对象的第一个元素
            const canvasId = $("#mycanvas")[0];
            const ctx = canvasId.getContext && canvasId.getContext("2d");
            ctx.beginPath();
            ctx.moveTo(75,25);
            ctx.quadraticCurveTo(25, 25, 25, 62.5);
            ctx.quadraticCurveTo(25, 100, 50, 100);
            ctx.quadraticCurveTo(50, 120, 30, 125);
            ctx.quadraticCurveTo(60, 120, 65, 100);
            ctx.quadraticCurveTo(125, 100, 125, 62.5);
            ctx.quadraticCurveTo(125, 25, 75, 25);
            ctx.stroke();
        }
    </script>
</body>
</html>